Method of preparing and nitriding a ferrous article



' April 9, 1935.

A. w MORRIS METHOD OF PREPARING AND NITRIDING A FERROUS ARTICLE Jen/e afb fh LL/l Original Filed Dec. 17. 1951 gwoeml'oz AM Marl-15s,

Patented Apr. 9, I 1935 PATENT OFFICE IWETHOD F PREPARING AND NITRIDING A FERROUS ARTICLE Albert W. Morris, Springfield, Mass., assignor to Moore Drop Forging Company, Springfield, Mass., a corporation of Massachusetts Original application December 17, 1931, Serial No. 581,701. Divided and this application August 25, 1934, Serial No. 141,515

4 Claims.

December 17, 1931.

Heretofore, so far as I am informed, in preparing a ferrous article for surface nitrogenization, all the metal'in the article has been made of the same mixture or alloy. In other words, to get a surface suitable for nitridation, the entire piece has been made of a nitridable alloy or of the same composition throughout its mass.

This generally is a disadvantage, first because of the cost, and second because the elements included in the article to make it nitridable are usually detrimental to the texture of the article and often interfere with or prevent heat treatment.

My improved method consists in impregnating the surface of the ferrous article to be treated to a suitable depth with a metal or alloy having aflinity for nitrogen. The article thus treated is then subjected to the action of nitrogen so that a hard nitrided surface will be obtained on the article and whereby the core or center of the article will be practically untreated'and' will retain the characteristics due to its original composition or alloy.

By my method almost any ferrous alloy having good properties of strength and that will be insensible to tempering brittleness can be used, thus insuring better castings, forgings and permitting heat treatment of ferrous articles having nitrided surfaces.

My method may be carried out as follows:- After making the ferrous article in the form .desired, either by casting or forging I immerse or dip it, while hot, and preferably heated to a temperature above 1200" Fahrenheit, in a bath of 40 molten metal having affinity for nitrogen. This bath is preferably molten aluminum either pure or alloyed with zirconium, titanium, chromium,

. vanadium, magnesium, beryllium, silicon, nickel,

molybdenum, manganese, or any desired combi- 45 nation of these, known in the art for alloying with iron to make up a nitridable alloy.

I have found by thus treatinga ferrous article that there will-be a surface impregnation thereof to a considerable depth by the metal or alloy hav- 50 ing aflinity for nitrogen.

I have also found that I can increase both the depth and amount of the impregnation of the ferrous article by subjecting the bath of molten metal having afflnity for nitrogen to the action 55 of electricity, by passing an electric current through the molten bath and the ferrous article.

The improved method may be carried out by many forms of apparatus, a preferred form being illustrated in the accompanying sheet of drawings forming part of this application for patent.

Referring to the drawing:

Fig. 1 is a sectional elevation of one form of apparatus.

Fig. 2 is a sectional elevation of another form of apparatus that can be used to practice my invention. 4

Referring more specifically to the drawing in which like reference numerals designate like parts, A designates a heating chamber, and B a suitable crucible which can be placed in the chamber A, the crucible havinglugs G which position the same in the heating chamber.

E designates a cover plate. which is adapted to rest upon the top rim of the chamber A. This cover plate may be tightly clamped to the top of the chamber by screws F, which are pivoted in the lugs G on the chamber and which screws fit between ears 0 formed on the rim of the cover plate E, nuts H being threaded on the screws F.

A packing or bearing washer may be placed on topof the chamber. The cover plate E may be provided with a stuffing box I through which a plunger J can be reciprocated for purposes hereinafter described. This plunger may be made of graphite or may have its surface coated with graphite. Extending from the cover plate is a notched flange K for holding the ferrous articles to be treated.

Practically any ferrous article can be treated in the apparatus above described. As shown a number of automobile shafts L are being treated. With the above described apparatus, the shafts L after being shaped either by forging or casting are placed in the notches in the flange K.

Care should be taken to keep the articles from touching each other, while in the bath, as such touching would hinder impregnation of the articles at the points of contact and would result in thin spots in the coating.

These shafts or ferrous articles to be treated when placed in position should be very hot, preferably heated to a temperature above 1200 Fahrenheit. This temperature can be obtained by taking the articles while they are hot from forging or casting or they can be heated to thedesired temperature before being placed in the notches.

The crucible is filled with a bath of molten metal or alloy having aflinity for nitrogen. The

metal or alloy thus employed is preferably aluminum or any alloy that is known in the art as useful for affecting nitrogenization.

The cover plate is then placed in position on the crucible and tightly clamped: thereto so that the hot ferrous articles will be immersed or dipped in the bath of molten metal. The articles are kept in the bath a suitable length of time. 4

During the treatment in the bath, care should be used to see that the surface of the ferrous articles to be impregnated are clean and free from scale.

I found that under these conditions, the metal or alloy having affinity for nitrogen will penetrate to a sufiicient depth into the surface of the ferrous articles being treated to permit them to be nitrided after being machined to size.

This impregnation may be accelerated by depressing the plunger J to create a hydrostatic pressure between the bath and the articles, al-

though this is not essential.

An electric heater is used to heat the bath and the electric current is led from the bath through the plunger J, or vice versa, the crucible being made out of material which will conduct electricity.

In Fig. 2 the electric circuit is connected to thefiange'which carries the ferrous articles so that the current will pass through the ferrous articles into the bath of molten metal, or vice versa, whereby the current will help, and increase the impregnation. The flange in this modification has a hub extending through a bushing Q of insulating material fitted in the cover plate ""E.

After the above treatment the cover plate is removed and the ferrous articles are allowed to cool. They then may be subjected to a finishing process such as grinding or machining to get the same to exact size.

Then the articles are subjected to the action of free or nascent nitrogen as in any ordinary nitrogenization or nitridation process.

Impregnation of surfaces not to be nitrided later may be prevented by protecting said surfaces by a suitable plating or paint. This also can be done after impregnation and before the time for nitridation. I

For example, all of the surfaces of the cam shafts under treatment in the apparatus, except the bearing surfaces may be protected so that the only surfaces which will be hardened or nitrided will be the bearings and the cams.

The nitrogen will unite with the metal having an afilnity for nitrogen which has impregnated into the surface of the ferrous article.

Thus a ferrous article will be produced having any desired ferrous composition in-its core anddescribed, and isparticularly adapted for heat treatment. a

While I have shown a preferred form of apparatus for practicing my improved method, other forms of apparatus may be devised whereby the surface impregnation, which is the principal feature of my invention, can be practiced, and I do not intend to be limited other than in the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States is: 1. The method oftreating a ferrous article, which consists in immersing the article while heated in a bath of molten metal having aflinity for nitrogen and composed at least in part of aluminum, to obtain a surface impregnation of the ferrous article with said metal, passing an electric current through said bath during immersion to obtain a surface impregnation of the ferrous article with said metal and thereafter removin the article from the bath and subjecting same to hardening by nitridation.

2. The method of treating a ferrous article. which consists in immersing the article while heated in a bath of molten metal having aillnity for nitrogen and composed at least in part of aluminum, to obtain a surface impregnation of the ferrous article'with said metal, passing an electric current through said bath ,and into said article or through said article into said'bath during immersion to obtain a surface impregnation of the ferrous article with said metal and thereafter removing the article from the bath and subjecting same to hardening by nitridation.

3'..The method of treating a ferrous article, which consists in heating the article to a temperature of at least 1200 F. and immersing the article while heated in a bath of molten metal having afllnity for nitrogen and composed at least in part of aluminum, to obtain a surface impregnation of the ferrous article with said metal, passing an electric current through said bath during immersion to obtain a surface impregnation of the ferrous article with said metal and thereafter removing the article from the bath and subjecting same to hardening by nitridation.

4. The method of treating a ferrous article, which consists in heating the article to a temperature of at least 1200 F. and immersing the nation of the ferrous article with said metal, passing an electric current through said bath and into said article or through said article into said bath during immersion to obtain a surface impregnation of the ferrous article with said metal and thereafter removing the article from the bath and subjecting same to hardening by nitridation.

w. MORRIS. 

